People love to see imagery all around them. Size, brightness, resolution, contrast ratio, 3D and many other features attract the attention of viewers. The goal in creating a display system is to create the best experience possible for the viewer. Creating the best experience often means optimizing the quality of the display. Quality factors include, but are not limited to, geometric accuracy, color accuracy, contrast, resolution, and freedom from distracting artifacts and other performance properties which contribute to the generally pleasing nature of the image. They may also include allowing the displayed digital image to accurately represent the original digital image or an image found in nature. To achieve the best possibly experience for the user, and/or quality of the display, it is desirable to correct for certain inaccuracies in the image produced by a display by applying corrective measures to image information and tuning the operating point of the display system.
Display systems are composed of one or more display units. Display units may be flat panel displays, projectors, emissive displays, e-ink displays, etc. They may be flat or curved. Examples of such displays are listed in U.S. patent application Ser. No. 12/049,267 entitled SYSTEM AND METHOD FOR PROVIDING IMPROVED DISPLAY QUALITY BY DISPLAY ADJUSTMENT AND IMAGE PROCESSING USING OPTICAL FEEDBACK, and U.S. patent application Ser. No. 12/818,102, entitled SYSTEM AND METHOD FOR INJECTION OF MAPPING FUNCTIONS whose disclosures are incorporated herein by reference as useful background information. Disadvantageously, each of these types of display units may suffer from different artifacts.
Flat panel type displays, for example, often suffer from color and intensity sheen within panels, and color and intensity differences across panels. They may also suffer from different input-output curves. For example, they might show the low intensity gray levels very similarly, but not high intensity gray levels. Undesirable geometric issues may also result due to bezels, misalignment of multiple-panels, desiring unusual display shapes within a panel, panels being aligned in shapes such as a cylinder, etc.
Projection-based displays suffer from geometric distortions, sometimes on a per-color channel, often as a result of imperfect optics in the projectors. They also suffer from intensity variations within and across projectors, color sheens, color mismatches across projectors, varying black levels, different input-output curves, etc.,
For the display of 3D images, often a different/discrete image is presented to the right eye and the left eye. Methods for accomplishing this task can include using time to alternate images delivered to each eye, using properties of the light such as polarization or wavelength to select which eye will receive a particular image, using optics to attempt to deliver a different image to each eye based on the eye's spatial location, etc. For 3D images, as with standard images, there may be geometric artifacts, color and intensity artifacts, and potentially different artifacts for the image intended for each eye.
Corrections made to the system can occur in many places in the chain of functions that carry out the displaying of the image. One example can occur in the creation of the digital signal, such as described in detail in the above-incorporated SYSTEM AND METHOD FOR INJECTION OF MAPPING FUNCTIONS. One example can be described in the projector or intermediate warping boxes, such as the OMTE parameters, such as described in detail in the above-incorporated U.S. patent application Ser. No. 12/049,267. For example, in some projectors it is contemplated to change the input/output curve of the projectors, for example for each color independently. By way of example, some display units have shading tables across the projectors that can be accessible to be changes. Often Liquid Crystal on Silicon (LCOS) projectors include this capability.
The types of corrections that are contemplated include warping imagery onto the screen. If using projectors, blending imagery across projectors so that the total intensity of a region overlapped by multiple projectors is similar intensity to the rest of the display. It is also contemplated that corrections for color and intensity changes can occur both across display units and within display units.
Many types of imagery can be shown on the scene. Sometimes the content is effectively a rectangular image that can be blended and warped onto the screen. Sometimes the content consists of many views of a three dimensional scene, where potentially each display unit may be given a different view of a three dimensional scene, and each display units stretches and warps the views so that the resulting display system appears to show one very large view of the entire system. In this case, the content is often rendered using a three-dimensional rendering engine such as OpenGL or DirectX.
Some more specific considerations in view of identified disadvantages of the prior art are provided as follows, by way of useful background:
OBSCURING FACTORS: Display systems in use often have dirt or other foreign matter on the screen. Optical sensors, such as cameras, often have dirt or other foreign matter on their lenses. There can be non-functional pixels on the display system, and non-functional pixels on cameras. For many display systems, turning the lights off in a room or closing the drapes on the windows to make the room dark is challenging. Thus, color data and intensity data collected during the calibration is often noisy, or is prone to small errors giving the obscuring factors. There can also be shiny metal frames or black borders around the desired region of interest so that pixels on the boundary can appear to be much brighter or dimmer than is appropriate. Cameras sensors are not perfectly characterized. It is desirable to provide appropriate algorithms and processes that had handle these obscuring factors and still produce a high quality display system.
CALCULATING: Brilliant color is an algorithm/process often used in display units such that input intensities sent to a display unit are non-linearly mapped to output color and intensity. The goal is often to make images appear brighter. Such mapping algorithms/processes are sufficiently non-linear that mapping out the entire input to output color and intensity mapping curve requires a significant amount of data, which can be time-consuming. Similarly, light reflecting from one portion of the screen to another is challenging to model; but without taking such effects into account makes it difficult to generate uniform intensity displays. It is desirable to provide an algorithm that accounts for all of these issues.
USER TRADE-OFFS: Display units often have intensity fall-offs at or near the edges. When this happens, finding an overall display system with uniform intensity can mean giving up a lot of brightness. Therefore, users typically prefer systems that are perceptually uniform, such as described in U.S. Pat. No. 7,038,727, entitled METHOD TO SMOOTH PHOTOMETRIC VARIATIONS ACROSS MULTI-PROJECTOR DISPLAYS” by Majumder et al., the teachings of which are incorporated by reference as useful background information. It is noted that slow intensity and color variations across a system are often not perceivable by humans. Allowing such variations rather than requiring uniform intensity typically results in a significantly brighter display.
In actual, commercially available display and imaging systems, users prefer to make trade-offs and understand the effects of their decisions. For example, in very bright rooms, users may choose the brightest display system possible, irrespective of the resulting uniformity (or lack thereof) of the display system. In very dark rooms, perceptual intensity smoothness can be far more significant. In other situations, users may prefer to make a trade-off between brightness and perceptual uniformity.
Similarly, users may often trade off speed of the calibration or calculation process for the accuracy of the results. Alternatively, users may often trade off brightness for color variations. Sometimes users have spatial preferences. For example, the region at the center of display system may need to be very uniform, but the need for uniformity in other regions of the system may be of less concern.
FAST RECALCULATION: As a system sits, the optical sensors or the display units can often move small amounts by being shaken or nudged. Collecting color and intensity data about the projectors from the optical sensors can be a time-consuming process—particularly because of the common desire to calibrate a system for both bright content and dark content, meaning that many training images may need to be captured to achieve a good display result during runtime. It is desirable for the system to be able to use previously collected data, and re-use it with a minimum amount of new data collection.
Thus, it is generally desirable to provide a calibration system for color and intensity that is practical for the user to handle and operate, handling obscuring factors, allowing the user to make trade-offs, and making it possible to recalculate a correction quickly and efficiently.